My last child is twelve i want another child im forty and healthy, what are my chances and options?

Your choice: If your general health is good & you don't need to take meds that would be toxic to baby the choice is yours to make. At 40 your risk of a baby with a chromosome defect increases to roughly 1% & that is added to a general risk of ~4% for unexpected outcome. A visit with a genetic counselor might provide a fuller picture, but all should be discussed with your obgyn.